Light emitting device, ranging device, and movable object

Abstract

A light emitting device includes: a first semiconductor light emitting element that includes a first active layer and a first resonator portion over a semiconductor substrate, and emits a first light; a second semiconductor light emitting element that includes a first reflector, a second resonator portion including a second active layer excited by the first light, and a second reflector stacked in this order over the first semiconductor light emitting element, and emits a second light, wherein an oscillation wavelength of the second semiconductor light emitting element is longer than that of the first semiconductor light emitting element, wherein the second semiconductor light emitting element includes a saturable absorption layer between the second resonator portion and the second reflector, and wherein a thickness L and an absorption coefficient α of the second active layer satisfy the following inequality. 3.45 ≤ α × L ≤ 15

What is claimed is: 
     
         1 . A light emitting device comprising:
 a first semiconductor light emitting element that includes a first active layer and a first resonator portion over a semiconductor substrate, and emits a first light;   a second semiconductor light emitting element that includes a first reflector, a second resonator portion including a second active layer excited by the first light, and a second reflector stacked in this order over the first semiconductor light emitting element, and emits a second light; and   a driving unit that injects a current into the first semiconductor light emitting element,   wherein an oscillation wavelength of the second semiconductor light emitting element is longer than an oscillation wavelength of the first semiconductor light emitting element,   wherein the second semiconductor light emitting element includes a saturable absorption layer between the second resonator portion and the second reflector, and   wherein a thickness L of the second active layer and an absorption coefficient α of the second active layer satisfy the following inequality.   
       
         
           
             
               
 
               
                 3.45 
                 ≤ 
                 
                   α 
                   × 
                   L 
                 
                 ≤ 
                 15 
               
             
           
         
       
     
     
         2 . The light emitting device according to  claim 1 , wherein the first semiconductor light emitting element includes a third reflector, a first resonator portion including the first active layer, and a fourth reflector stacked in this order over the semiconductor substrate. 
     
     
         3 . The light emitting device according to  claim 1 , further comprising a carrier blocking layer formed between the second resonator portion and the saturable absorption layer. 
     
     
         4 . The light emitting device according to  claim 1 , wherein the second active layer has a thickness such that an amount of absorption of the first light is 90% or more. 
     
     
         5 . The light emitting device according to  claim 1 , wherein the thickness L of the second active layer and the absorption coefficient α of the second active layer satisfy the following inequality. 
       
         
           
             
               
 
               
                 4.2 
                 ≤ 
                 
                   α 
                   × 
                   L 
                 
                 ≤ 
                 7.5 
               
             
           
         
       
     
     
         6 . The light emitting device according to  claim 1 , wherein the thickness L satisfies the following inequality. 
       
         
           
             
               
 
               
                 
                   2.3 
                       
                   µm 
                 
                 ≤ 
                 L 
                 ≤ 
                 
                   10 
                   ⁢ 
                       
                   µm 
                 
               
             
           
         
       
     
     
         7 . The light emitting device according to  claim 1 , wherein the thickness L satisfies the following inequality. 
       
         
           
             
               
 
               
                 
                   2.8 
                     
                   µm 
                 
                 ≤ 
                 L 
                 ≤ 
                 
                   5 
                   ⁢ 
                       
                   µm 
                 
               
             
           
         
       
     
     
         8 . The light emitting device according to  claim 1 , wherein the second semiconductor light emitting element is configured to emit the second light having a profile that has a maximum peak value and converges to a stable value that is a predetermined light intensity after the maximum peak value. 
     
     
         9 . The light emitting device according to  claim 1 , wherein the second active layer includes a plurality of quantum well layers. 
     
     
         10 . The light emitting device according to  claim 9 , wherein the plurality of quantum well layers are located at antinode positions of a standing wave generated in the second active layer. 
     
     
         11 . The light emitting device according to  claim 9 , wherein a center of gravity of the plurality of quantum well layers is located at a center in a thickness direction of the second active layer. 
     
     
         12 . The light emitting device according to  claim 9 , wherein a center of gravity of the plurality of quantum well layers is located on a side of an end of the second active layer from which the first light enters the second active layer rather than a center in a thickness direction of the second active layer. 
     
     
         13 . The light emitting device according to  claim 1 , wherein the saturable absorption layer includes quantum well layers and barrier layers formed above and below each quantum well layer, and
 wherein a band gap of the barrier layer is greater than or equal to an energy of the first light.   
     
     
         14 . The light emitting device according to  claim 13 , wherein the barrier layer is formed of InP or InGaAsP. 
     
     
         15 . The light emitting device according to  claim 1 , wherein the second active layer includes a quantum well layer and barrier layers formed above and below the quantum well layer,
 wherein the barrier layer is formed of InGaAsP, and   wherein the quantum well layer is formed of InGaAs.   
     
     
         16 . The light emitting device according to  claim 1 , wherein the first semiconductor light emitting element includes a plurality of first light emitting portions that emit the first light. 
     
     
         17 . The light emitting device according to  claim 16 , wherein a first light emitting portion of the plurality of first portions includes the first active layer shaped in a mesa. 
     
     
         18 . The light emitting device according to  claim 16 , wherein the plurality of the first light emitting portions are arranged in a two-dimensional array. 
     
     
         19 . The light emitting device according to  claim 16 , wherein the second semiconductor light emitting element includes a plurality of second light emitting portions that emit the second light corresponding to the plurality of first light emitting portions. 
     
     
         20 . The light emitting device according to  claim 1 , further comprising a light receiving element that receives the second light emitted from the second semiconductor light emitting element. 
     
     
         21 . A ranging device comprising:
 the light emitting device according to  claim 1 ;   a light receiving device configured to receive light emitted from the light emitting device and reflected by an object to be measured; and   an acquisition unit configured to acquire information on a distance to the object to be measured based on a time difference between a timing at which light is emitted from the light emitting device and a timing at which light is received by the light receiving device.   
     
     
         22 . A movable object comprising:
 the ranging device according to claim  21 ; and   a control unit configured to control the movable object based on information on the acquired distance.